175 
Among the Hymenopterous insects which assist in destroying plant- 
lice, none perhaps are more affective than certain very minute Ichneu¬ 
mon flies, which have received the name Aphidides from the fact that 
they are parasitic upon the Aphides or plant-lice. 
These little insects, which seldom reach one-tenth part of an inch in 
length, are wasp-like in shape, furnished with four tiny wings with 
three cubital cells in the anterior ones; mostly black bodies, variously 
adorned with bright yellow bands and other marks; the second and 
third segments ot the abdomen move freely upon each other. When 
one is about to deposit her eggs she approaches and touches a plant- 
louse with her long slender antennae, and is enabled thereby to de¬ 
termine with certainty whether it has received an egg; if not, she at 
once punctures the body with her slender ovipositor and deposits an 
egg therein, and passes on to another to repeat the operation. This 
egg produces a minute grub or larva, which ultimately destroys the life 
of its victim, and comes forth a fly, similar to its parents. 
The description of a few species will be sufficient to convey to the 
reader an idea of these useful insects, which is all that is necessary 
for present purpose. 
Aphidius lactucaphis, Fitch. Lettuce-louse Aphidius. 
Deep black, legs trimmed with brownish; antennae 19-jointed, second 
joint smallest, globular, third joint longest, with a slight constriction 
in the middle; wings slightly smoky, outer marginal vein and vein 
bordering the cell beyond the stigma, black, outer veins brown, stigma 
white; abdomen long obovate, flattened, rather narrower than the 
thorax, tip rounded. Length, 0.06. inch. 
The names given indicate the species of Aphis upon which these 
insects are known to be parasitic. But it is not probable they are con¬ 
fined to a particular species. 
Aphidius (Praon) polygonaphis, Fitch. The Knot-weed-louse 
Aphidius. 
Black and shining; abdomen slender elliptical, of a bright sulphur 
yellow color; tinged with dusky above and beneath the tip, with broad 
yellowish bands at the anterior sutures, base narrowed to a short ped¬ 
icel, which, with the legs and base of the antennae, are reddish yellow; 
antennae 17-jointed. Length 0.08 inch. 
Aphidius (Praon) viburnapiiis. Fitch. Cranberry-louse. Aphidius. 
Black and shining; similar to the preceding, but the abdominal 
pedicel and the legs only yellowish; antennae 15-jointed. 
